It’s 10 a.m. on a warm August morning in Regent Park, a neighborhood in the east end of downtown Toronto that has historically been defined by its public housing and poverty. Nadha Hassen, a junior fellow at Toronto’s Wellesley Institute, and her colleagues are here hosting a walking tour to get residents of Regent Park out to talk about how parks interact with mental health, both individually and across the community.

Except the residents aren’t showing up. Hassen is fighting hard to put on a positive face, but she seems concerned while repeatedly checking her phone. Word eventually comes in: gunshots in the early hours of the morning have spooked many people in the community, and an emergency meeting is being held to assess the situation. As the 505 Dundas streetcar rumbles by, the large park at the center of the entire neighborhood is virtually empty. The walking tour (which Hassen calls a WalkLab) proceeds with more facilitators and reporters than guests. But considering the topic at hand—how to measure the quality of parks as they interact with the broad mental health of a neighborhood—those absences speak just as loudly as anybody in attendance.

It is a familiar story for residents of the neighborhood, where unemployment, poverty, and social assistance are daily realities. Forty-six percent of Regent Park’s population are classified as low-income—almost two-and-a-half times the city average—and 16 percent of neighborhood residents are unemployed.

Regent Park and its socioeconomic challenges stand in stark contrast to the neighborhoods surrounding it, many of them hot spots for gentrification. To the north sits Cabbagetown. It and Regent Park were once considered one in the same, but are now divorced both in name and economic trajectory. To the south is the Distillery District, a heritage neighborhood filled with bars, restaurants, and high-end shops.

At the center of Regent Park is, as the name suggests, a park. By downtown Toronto standards, it’s a large one. Along with the new community center that sits on its east side, it takes up an entire large city block. In 2011, the park and the community center were redeveloped as part of a 15-year, $561-million revitalization project approved by Toronto’s City Council in 2003 and started in 2005.

However, ten years into the larger project, it’s hard to quantify its overall success: there’s no recent census data to measure any improvement in health outcomes, incomes, or social equality. A 2014 aggregate score released by the City of Toronto called the “Neighbourhood Equity Indicator” showed Regent Park with the 8th-worse worst score in the city. Despite the promises made by the revitalization project to “reinvent” Regent Park, the latest data from 2011 ranks it as one of the poorer neighborhoods in Toronto. (Construction has displaced many residents of the neighborhood, making an assessment of the social effects of the revitalization plan next to impossible.) Much of the first phase of development focused on the city park at the heart of the neighborhood—which is what brings Hassen and her colleagues to the park to try to understand how park development like this affects the mental health of residents.

It’s an oft-repeated maxim—even among planners and designers—that parks are good for mental health. In Toronto, for example, the 2013 Official City Parks Plan reads, “access to green space reduces stress level, decreases negative mood, reduces feelings of depression, and provides other benefits to mental health and well-being.”

City officials often talk about the relationship as if it’s beyond doubt. But academic research is split on the relationship between parks and mental health. “Empirical evidence is much more limited than one would expect for such a straightforward question,” write Roland Sturm and Deborah Cohen in their 2014 paper, “Proximity to Urban Parks and Mental Health.” Their study suggests that moving to an area with more green space tends to improve one’s mental health, while moving to an area with less has the opposite effect. But one year later in a paper titled, “The Relationship between Natural Park Usage and Happiness Does Not Hold in a Tropical City-State,” authors Le Saw, Felix Lim, and Luis Carrasco found “no significant relationship between well-being and use of green space as well as proximity to green spaces. […] This study reveals that without first considering the critical factors that permit this relationship to occur, it will be premature to conclude that an increase in green space provision will lead to a direct increase in well-being.”

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Toronto is an instructive entry point to look at the limitations inherent in drawing links between mental health and the amount of green space in a given neighborhood. According to data from Urban HEART Toronto, among the top 25 percent of neighborhoods in the city (as ranked by the amount of accessible green space) the average mental health score is actually marginally lower than in the bottom 25 percent: 72.1 to 73.5, respectively. Similar ambiguity exists when the data is approached in reverse: the top 25 percent of neighborhoods, ranked by mental health scores, have barely more green space on average than do the bottom 25 percent. Areas like Thorncliffe Park, which has the second-highest amount of green space in the city, is in the middle of the pack in terms of mental health; more striking is Elms-Old Rexdale, which has the highest city-wide green space score and the 17th-worst mental health score.

This data is not without its flaws—self-reporting mental health is notoriously unreliable (“It’s not great, but it’s something,” says Hassen). The data does make some points abundantly clear—namely, that it is very difficult to prove correlation between parks and mental health.

“To just say that green space is good for mental health is completely simplistic,” says Hassen. “We have to go beyond that.” Her research at the Wellesley Institute aimed at developing a theoretical framework in which to assess quality of green space—an indicator that proves difficult to measure accurately. While city planners are used to assessing quantity of available land and accessibility, a third measure of the quality of the space is often left out of the picture, in part because it is difficult to measure objectively, and because how it factors into larger urban questions is not well understood.

Interestingly, Hassen’s preliminary findings suggest that poorly planned parks have the capacity to actually worsen the mental health outcomes in some places, effectively doing the opposite of one of their intended functions. The reason seems obvious: in neighborhoods facing larger social issues like drug usage and crime, parks can simply serve as a place for these things to coagulate. But that isn’t an argument against building parks in low-income neighborhoods. “It just needs to be done in a way that is aware of the issues in the community,” says Hassen. “You want it to be safe. You don’t want it to be this off-to-the-side place that people avoid because they know that bad things happen there.”

In neighborhoods like Regent Park, where poverty and crime are perceived as problems, negative incidents—such as the reports of gunshots that seemed to have kept people from the WalkLab—contribute to a subtle recasting of the role of the park in the community. Parks become catalysts for disruptive influences, rather than community-building.

It’s this kind of nuanced thinking that often doesn’t make it as far as official planning documents. Careful thinking about green space in terms of mental health outcomes is “not something that has been factored in in a more systematic way, says Ronald Macfarlane, manager of Healthy Public Policy at Toronto Public Health. Research into the relationship is a fairly new area of study. Parks People, an independent charity that advocates for park development in Toronto, is releasing a research report into social development and parks in February 2017. “From the research that we’ve looked at for our Sparking Change report, it’s very clear that a key driver of positive social [and] community benefits in parks, including mental health, is high-quality, well-maintained parks that have activities that bring people together and reduce social isolation. It’s not enough to have a patch of green if no one uses it or feels comfortable there,” says Jake Tobin Garret, manager of policy and research for Park People.

While Toronto’s parks department declined requests for comment, Toronto Public Health was quick to note, despite publishing a review of literature supporting the notion that green space has a positive effect on mental health, the relationship is not well understood. “Green space is starting to be seen as a real asset, and an asset we need to maintain,” says Macfarlane. But, he adds, “mental health has not been a major aspect of it.” For public health officials, there are too many variables when it comes to the relationship. “Part of the challenge is that when you’re talking about mental health and green space, a small green space may be sufficient and a large green space may be sufficient,” says Macfarlane. “A single tree somewhere can be very beneficial, if that’s the only thing you have around you. […] But for some people, going into green spaces can actually be frightening, So it’s not necessarily universal, either.”

At the core of this is a simple problem: creating policy when it comes to mental health is challenging. Like many social indicators (such as poverty or addiction levels), mental health is both part of a larger network of social determinants and a product of them, as well. And so the claims that parks are good for mental health, while it may be true for the individual, are hard to scale to the community level. “Part of that is that mental health is tricky,” says Hassen. “What can complicate the relationship between public green space and mental health is that maybe those social determinants have stronger relationships.”

It isn’t enough to build parks—even numerous, sizable ones—and hope that health outcomes improve; the positive mental health benefits often associated broadly with green spaces and the outdoors depend on many factors. Some of them, like careful assessment of park features, qualities, and programs, are within the control of city parks departments. Others, like crime, drug use, and economic prospects, are not. Parks policies are not as simple as the “intuitive” claims we make about green space lead.

Neighborhoods like Regent Park encapsulate a difficult reality, one that is often at odds with the perceptions of parks: that the neighborhoods with the most green space are not always the healthiest. Green space does not inherently reduce the issues that hit downtrodden neighborhoods the hardest. But quality green space—that is, green space that is designed with improving mental health in mind (even if those mechanisms are not yet well understood)—can.

What is necessary, though, is for parks advocates and city officials to acknowledge that the simplistic terms through which they think about parks need to be complicated and expanded. To create parks with mental health in mind means trying to understand the mechanics of mental health itself. Embracing the difficulties of that question will lead to better parks and, hopefully, happier people.

Correction: A previous version of this article misspelled Nadha Hassen’s name.